In the recent years, ROADM (Reconfigurable Optical Add/Drop Multiplexer) techniques have been devised to increase the speed and capacity of optical communication. In an optical network using the ROADM, a wavelength multiplexing transmission method is used, and an optical signal of any wavelength can be added and dropped without being converted to an electric signal. Moreover, in the optical network using the ROADM, when a route through which an optical signal of each wavelength is to be transmitted is desired to be changed (newly added or disused), the route can be changed, i.e. reconfigured without performing work such as connection work (Reconfigurable).
In order to achieve the ROADM, there is required a switch device (also called multicast switch) which is provided between the ROADM network and a client device and which is capable of receiving and outputting multiple wavelengths and changing routes. Specifically, the switch device used in the ROADM has a function of receiving an input of an optical signal from the client device and adding the optical signal to a path of the ROADM network (hereafter, also referred to as Add function) and a function of outputting an optical signal dropped from a path of the ROADM network to the client device (hereafter, also referred to as Drop function), and is capable of dynamically changing the route through which the optical signal is transmitted. In this specification, the number of paths of the ROADM network to which the switch device is connectable is referred to as the number of paths, and the number of client devices to which the switch device is connectable is referred to as the number of wavelengths. Moreover, a series of routes (including waveguides and optical fibers) through which an optical signal inputted to or outputted from each path is transmitted is referred to as a channel.
FIG. 18 is a top view of an example of a switch device (multicast switch) 900 which has a dual configuration (i.e. a configuration with the Drop function and the Add function) and in which the number of paths is 8 and the number of wavelength is 16. The switch device 900 includes two splitter portions 920 and eight switch portions 930 in a housing 960. Each of the splitter portions 920 has a predetermined number of optical splitters, and each of the switch portions 930 has a predetermined number of optical switches. One ends of the splitter portions 920 are connected to the ROADM network via network-side fibers 940, and other ends thereof are branched and connected to one ends of the switch portions 930. Furthermore, other ends of the switch portions 930 are connected to the client devices via client-side fibers 950. The splitter portions 920 are connected to the switch portions 930 by a not-illustrated shuffle fiber array including multiple optical fibers which are three-dimensionally arranged. Such a configuration enables the switch device 900 to add and drop optical signals between the ROADM network and the client devices.
The switch device 900 is designed to process a predetermined number of wavelengths and a predetermined number of paths. Accordingly, in the case of changing the number of processable paths or wavelengths, the entire housing 960 needs to be replaced. In other words, the switch device 900 has poor extensibility and versatility, and requires huge cost to change the number of processable paths or wavelengths.
A configuration like that of a wavelength selective optical switch in Patent Document 1 can be employed to secure extensibility. Note that the wavelength selective optical switch in Patent Document 1 has a configuration similar to the multicast switch in the present invention, but is not a multicast switch. This is because a route through which an optical signal of each wavelength is to be transmitted is fixed in the wavelength selective optical switch, while a route for an optical signal of each wavelength is changeable in a multicast switch. The wavelength selective optical switch in Patent Document 1 includes a base unit and an extension unit, and the number of output ports can be increased by connecting the extension unit to the base unit in cascade.